Conventionally, a bar code reader for a POS (Point of Sales) system reads a bar code by the following method.
A bar code consisting of black bars 20 and white spaces 21, printed on paper as shown in enlarged section along the scanning direction in attached FIG. 7, is irradiated by light beams 200 from a light source (not shown).
The light beam 200 incident on the bar 20 is reflected and diffused on the surface of the bar 20. The surface of the bar 20, in case of in black color, provides a low reflectance. Consequently, the luminous intensity of light reflected on the bar surface to form an image in an image sensor or photoelectric conversion device (such as CCD) is extremely low.
Meanwhile, the light beam 200 incident on the space 21 is also reflected and diffused on the space surface in the same manner as in the black bar 20. Because the surface of the white space 21 provides a high reflectance, the luminous intensity of light (reflected light beam 201) reflected on the space surface to form an image in the image sensor is higher than that of the reflected light from the surface of the bar 20. Thus, the bar code reader identifies bars 20 and spaces 21 based on the difference in the luminous intensity of reflected light beams received by the image sensor, thereby reading bar code information.
Further, the conventional bar code reader for performing the above-described operation is designed to overcome the following drawback.
When the bar code surface is covered with a colorless, transparent laminate or vinyl film, and when the reflection light beam from the bar code surface to form an image in the image sensor is a regular or mirror reflection component, the bar code reader cannot read information, due to halation in the image sensor caused by the excessively high luminous intensity of the reflected light beam.
This problem has been .solved in the conventional bar code reader by designing a housing shape of the bar code reader and the internal optical system layout, so that an optical image is formed in the image sensor not by a regular reflection component but by a diffusion reflection component. As a result, the conventional bar code reader can read bar code information by the aforementioned method even when the bar code surface is covered with colorless, transparent film.
As POS systems and FA systems using the above-mentioned conventional [bar code readers have been spreading in recent years, integrated management of metal products on the basis of bar codes marked directly (by baking etc.) on the products has been increasing (For example, if scalpels for surgical operation bear bar codes on the surface, it is possible to distinguish sterilized scalpels from unsterilized ones, or to determine the sterilizing date of a particular scalpel by bar code). Accordingly, demand has been increasing for an information reading apparatus capable of accurately reading bar codes provided on metal products.
However, the conventional bar code reader described above is designed to form an image in the image sensor by the diffusion reflection component, and not by the regular reflection component of the light reflected on the bar code surface. Therefore, if the conventional bar code reader is used in an attempt to read a bar code on the specular surface of the metal product that provides the regular reflection component of a high luminous intensity, it is not possible to read the bar code by the ordinary method (that is, by placing the reading opening in contact with the bar code surface), due to the low luminous intensity of the diffusion reflection component.
In view of this problem of the conventional bar code reader, to an object of the present invention is to provide an information reading apparatus capable of at least reading optical information formed on a surface that, when light is incident, reflects light whose regular reflection component has higher luminous intensity than that of the diffusion reflection component.